The following descriptions and examples are not admitted to be prior art by virtue of their inclusion in this section.
In many well applications, valves are positioned downhole in the well to control the flow of various fluids, such as production fluids or injection fluids. The flow control valves are actuated by pressurized hydraulic fluid delivered downhole through control lines. A given well application may require multiple flow control valves with a plurality of control lines coupled to each valve to control actuation of the valve between states. However, space constraints in the wellbore can restrict the number of control lines that are routed downhole.
Multidrop systems have been developed in which the number of control lines is less than the number of flow control valves. In one example, a device is used which allows the selection of a specific downhole well tool via the use of different pressure levels. Hydraulic control signals are furnished at relatively low pressures to actuate a selected well tool, and the hydraulic pressure is selectively increased over a threshold level to provide hydraulic power to the well tool. The hydraulic control actuation signals may be controlled by selectively pressurizing different hydraulic lines in a selected sequence and by selectively controlling the fluid pressure within a specific hydraulic line. The combination of selective sequential actuation and selective fluid pressure provides multiple actuation combinations for selectively actuating downhole well tools. However, the use of two or more pressure levels can restrict operation of the system in subsea wells and also can limit the potential number of downhole tools utilized in a single downhole string.